Water Turbine
The waterwheel is an ancient technology that converts the energy of rushing water to human use. Mostly used for milling grain in ancient times, the simplest waterwheel has a series of submerged paddles fanning out from a vertical shaft. The moving water rotates the paddles and shaft, which passes through a fixed millstone and is fastened to a movable millstone on top. The more familiar traditional form employs a vertical wheel and horizontal shaft.
With the growing mechanization of the production process in the 1800s came an increasing demand for energy. Steam engines were feasible only where coal was cheap, and the old waterwheels did not make efficient use of available hydrological power. An urgent need to improve the efficiency of waterwheels was felt particularly in countries that had little or no coal. The first improvements were made by the Frenchman Jean Victor Poncelet (1788-1867), who proposed curbed blades and the use of iron instead of wood for the wheel itself. Wheelpits were built of masonry to form a tight enclosure around the wheel and force all the water coming through the millrace through the wheel.
In 1828, another Frenchman, Claude Burdin, coined the word turbine, from the Latin turbo , or spinning top. Burdin was a teacher at St. Etienne and taught a course on waterwheels. One of his students, Benoit Fourneyron, introduced the most momentous design changes in 1833. Fourneyron developed an enclosed water turbine that used two wheels. The wheels were completely submerged, and the inner, fixed wheel had gates that channeled the water to the blades of the outer rotating wheel, greatly improving the efficiency of the machine. By 1837, he had developed a design that was four times more efficient than the traditional waterwheel.
The design pioneered by Fourneyron was what has now come to be called a reaction turbine and was most efficient with fast-flowing water. Reaction turbines in use today are of several types, according to the available water pressure. The Francis type, developed by James Francis and Uriah Boyden in the 1850s, has an outside casing with guide vanes that simultaneously directed water against all the spirally curved vanes on the inner rotor. It is best suited for medium water pressures. The Kaplan type reaction turbine, produced by V. Kaplan in 1920, has four very large blades on an outer rotor in a design very similar to Fourneyron's. However, the pitch of the blades can be altered during the actual running to get the best results from varying water pressures. This latter type is most commonly used with low pressure. Finally, the Deriaz type combines features of the other two.
Where a small volume of water falls a great distance, the Pelton wheel, or impulse turbine, is most commonly used. It was invented by Lester Pelton, an American engineer who learned of waterwheels during the California gold rush. His device involves high-pressure water jets which are directed against the rim of a wheel fitted with large twin buckets.
Water turbines, an important feature of the Industrial Revolution, gradually made way for the more powerful and efficient steam turbines of the late 19th century. Turbine technology has also come to be used in jet propulsion, and has revolutionized aviation in the second half of the 20th century. Today water turbines no longer serve to drive industrial machinery directly, except in developing nations. However, they are still in use in hydroelectric plants. Natural waterfalls and dams provide falling water to power arrays of water turbines which are hooked up with electric generators. The energy is then distributed across vast electrical networks. A significant share of global energy consumption is contributed by this clean and cheap form of power.
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